1. Field of the Invention
This invention concerns improvements in or relating to strata movement indicators.
2. Description of Related Art
In particular the present invention has reference to indicators of the type described in United Kingdom Patents Nos 2 253 707 and 2 268 809 for use in underground mines in which an indicator element is suspended from an anchor within a borehole in the strata, the element registering with a guide fixed in the mouth of the borehole. The degree of extension of the element from the guide is equal to the strata movement.
These earlier indicators provided a simple and yet effective visual means of illustrating strata movement, but their usefulness was limited to employment in workings of relatively low height thereby allowing ready inspection. However, in areas where the roof height is above that for which parallax-free, close approach is practicable, the accuracy of reading is reduced. The problem is even greater when, for a high roof, the allowable movement is small.
An object of the invention is therefore to provide an improved means of indicating strata movement in terms of accuracy, sensitivity and ease of visibility from floor level.
A further object of the invention is to provide such means whereby the effect of strata movement is amplified and displayed with minimum parallax for an observer at floor level.
According to the invention a strata movement indicator includes a flexible suspension member, an anchor for anchoring the suspension member in use within a borehole, a drive element carried by the suspension member and extending in use generally within the mouth of the borehole, a reference element interengaging the drive element, a first indicator means associated with the drive element, a second indicator means associated with the reference element, whereby in use strata movement occasions substantially relative linear motion as between the drive element and the reference element and the said interengagement effects rotary motion as between the first and second indicator means to provide a visual indication of the extent of strata movement as given by the said relative motion.
The visible indication is advantageously amplified to facilitate reading by an observer from floor level.
In a first embodiment of the invention the drive element is provided with engagement means which may be in the form of a profiled protrusion interengaging the reference element which is adapted for fixture within the mouth of the borehole and is provided with a slot for engaging the protrusion, whereby in use upon relative linear movement between the drive and reference elements rotary motion is occasioned thereto to give relative movement as between the first and second indicator means, such movement providing an indication of the movement of the drive element and thus of the strata. The first indicator means may be in the form of a pointer and the second indicator means may be in the form of a circular scale or vice versa. The scale is preferably calibrated to give a visual indication of the extent of linear movement and the calibration may be in chromatic sector form or may provide actual measurement or may be a combination of both, the scale being of sufficiently large dimension as to be readable from floor level.
The drive element of the first embodiment may be formed with two or more slots engaging the protrusion thereby to provide stability in use during movement.
In a second embodiment of the invention, the drive element is provided with engagement means in the form of a guide slot for engagement with the reference element which is adapted for fixture within the mouth of the borehole and which has a profiled protrusion mating with the slot in such manner that relative linear movement also causes rotation of the drive element and also of the first indicator means in relation to the second indicator means. As an example, the protrusion may be helically profiled whereby by virtue of the interengagement of the slot with the protrusion, relative linear movement forces the drive element to rotate taking a helical path thereby causing the first indicator means to move in relation to the second indicator means. As with the first embodiment, two or more slots may be provided for stability. The protrusion may be aligned axially of the borehole or may be offset therefrom.
The first and second indicator means of the second embodiment may be of the same type as for the first embodiment.
The first and second indicator means are disposed relatively closely to the mouth of the borehole which may be formed in the roof of a mine roadway or other working site, or other civil engineering environment.
In a further embodiment of the invention, two or more suspension wires may be provided with the associated features of either the first or second embodiments or a combination of both, each wire being anchored at a different point along the length of the borehole thereby to provide an indication of strata movement at each point.